Urban Gardener: Is It OK to Reuse Potting Soil?

Whether potting spring bulbs or transplanting seedlings to a window box, the urban gardener has to answer a basic container-gardening question: Is it OK to re-use last year’s potting soil? Or should I start fresh?

The most basic answer is that yes, it’s possible to reuse last year’s soil. But first do a few things to perk it up–and replace its nutrients. Here’s how:

First, remove any plant matter (roots, twigs, leaves) from last season. I plucked from the window box the dried up winter greens I had used to decorate it in January.

OK. ready to begin the soil remediation. Basic science tells us that plants use the nutrients in soil to grow. Over time, reusing the same potting soil in container gardening can deplete the nutrient stores in the soil and result in lackluster plants. Luckily, there’s no need to do a wholesale soil dump each spring.

To prep the box, I used a trowel to turn my soil. Turning the soil had the dual purpose of making sure that it wasn’t invested with bugs–in which case a dump might be worth it-–and making sure that the soil is light and fluffy. Hard and compacted soil doesn’t leave enough room for roots to grow, so this step is crucial. Use a sturdy trowel; mine is a DeWit Garden Hand Shovel ($29 from Kaufmann Mercantile).

After I “tilled” my window box soil, I added a soil amendment. From a local shop, I bought a small bag of Plant-Tone Organic Plant Food (a 4-pound bag is $8.32 from Amazon). The mixture is an organic blend of bone meal, feather meal, poultry manure, and other stuff that smells a little funny but will return to the soil the nutrients that it might have lost. Alternately, you can add compost that you blend yourself at home or purchase from a farmer friend.

I added about a cup and half of plant food to my soil and mix it well. This is definitely an occasion for breaking out the garden gloves: mine are Gardener’s Goat Skin Work Gloves, $36 from Womanswork. I knew that I’d be adding potted plants with fresh soil already attached to their roots, so at this stage I scooped out some of the old soil to make room.

I gently separated some of the root bulbs from the mass to be able to fit them into my narrow box. Daffodil bulbs are hardy, so a little wriggling shouldn’t do any lasting damage.

I did the work on a backdrop of brown paper bags, opened up so that after I finished I could dump any leftover soil into my soil storage bag and not leave too much of a mess behind.